Historiometry The method used in
Hereditary Genius has been described as the first example of
historiometry. To bolster these results, and to attempt to make a distinction between 'nature' and 'nurture' (he was the first to apply this phrase to the topic), he devised a questionnaire that he sent out to 190
Fellows of the Royal Society. He tabulated characteristics of their families, such as
birth order and the occupation and
race of their parents. He attempted to discover whether their interest in science was 'innate' or due to the encouragements of others. The studies were published as a book,
English men of science: their nature and nurture, in 1874. In the end, it promoted the
nature versus nurture question, though it did not settle it, and provided some fascinating data on the sociology of scientists of the time.
The lexical hypothesis Galton was the first scientist to recognise what is now known as the
lexical hypothesis. This is the idea that the most salient and socially relevant personality differences in people's lives will eventually become encoded into language. The hypothesis further suggests that by sampling language, it is possible to derive a comprehensive taxonomy of human
personality traits.
The questionnaire Galton's inquiries into the mind involved detailed recording of people's subjective accounts of whether and how their minds dealt with phenomena such as
mental imagery. To better elicit this information, he pioneered the use of the
questionnaire. In one study, he asked his fellow members of the Royal Society of London to describe mental images that they experienced. In another, he collected in-depth surveys from eminent scientists for a work examining the effects of nature and nurture on the propensity toward scientific thinking.
Variance and standard deviation Core to any statistical analysis is the concept that measurements vary: they have both a
central tendency, or mean, and a spread around this central value, or
variance. In the late 1860s, Galton conceived of a measure to quantify normal variation: the
standard deviation. Galton was a keen observer. In 1906, visiting a livestock fair, he stumbled upon an intriguing contest. An ox was on display, and the villagers were invited to guess the animal's weight after it was slaughtered and dressed. Nearly 800 participated, and Galton was able to study their individual entries after the event. Galton stated that "the middlemost estimate expresses the
vox populi, every other estimate being condemned as too low or too high by a majority of the voters", and reported this value (the
median, in terminology he himself had introduced, but chose not to use on this occasion) as 1,207 pounds. To his surprise, this was within 0.8% of the weight measured by the judges. Soon afterwards, in response to an enquiry, he reported the mean of the guesses as 1,197 pounds, but did not comment on its improved accuracy. Recent archival research has found some slips in transmitting Galton's calculations to the original article in
Nature: the median was actually 1,208 pounds, and the dressed weight of the ox 1,197 pounds, so the mean estimate had zero error. James Surowiecki uses this weight-judging competition as his opening example: had he known the true result, his conclusion on the
wisdom of the crowd would no doubt have been more strongly expressed. The same year, Galton suggested in a letter to the journal
Nature a better method of cutting a round cake by avoiding making radial incisions.
Experimental derivation of the normal distribution Studying variation, Galton invented the
Galton board, a
pachinko-like device also known as the bean machine, as a tool for demonstrating the
law of error and the
normal distribution.
Bivariate normal distribution He also discovered the properties of the
bivariate normal distribution and its relationship to
correlation and
regression analysis.
Correlation and regression In 1846, the French physicist
Auguste Bravais (1811–1863) first developed what would become the correlation coefficient. After examining forearm and height measurements, Galton independently rediscovered the concept of
correlation in 1888 and demonstrated its application in the study of heredity, anthropology, and psychology. Galton's later statistical study of the probability of extinction of surnames led to the concept of
Galton–Watson stochastic processes. Galton invented the use of the regression line and for the choice of r (for reversion or regression) to represent the correlation coefficient. In the 1870s and 1880s he was a pioneer in the use of
normal theory to fit
histograms and
ogives to actual tabulated data, much of which he collected himself: for instance
large samples of sibling and parental height. Consideration of the results from these empirical studies led to his further insights into evolution, natural selection, and regression to the mean.
Regression toward the mean Galton was the first to describe and explain the common phenomenon of
regression toward the mean, which he first observed in his experiments on the size of the seeds of successive generations of sweet peas. The conditions under which regression toward the mean occurs depend on the way the term is mathematically defined. Galton first observed the phenomenon in the context of
simple linear regression of data points. Galton developed the following model: pellets fall through a
quincunx or "
bean machine" forming a normal distribution centred directly under their entrance point. These pellets could then be released down into a second gallery (corresponding to a second measurement occasion). Galton then asked the reverse question "from where did these pellets come?"
Theories of perception Galton went beyond measurement and summary to attempt to explain the phenomena he observed. Among such developments, he proposed an early theory of ranges of sound and
hearing, and collected large quantities of anthropometric data from the public through his popular and long-running Anthropometric Laboratory, which he established in 1884, and where he studied over 9,000 people. It was not until 1985 that these data were analysed in their entirety. He made a beauty map of Britain, based on a secret grading of the local women on a scale from attractive to repulsive. The lowest point was in
Aberdeen.
Differential psychology Galton's study of human abilities ultimately led to the foundation of
differential psychology and the formulation of the first mental tests. He was interested in measuring humans in every way possible. This included measuring their ability to make sensory discrimination which he assumed was linked to intellectual prowess. Galton suggested that individual differences in general ability are reflected in performance on relatively simple sensory capacities and in speed of reaction to a stimulus, variables that could be objectively measured by tests of sensory discrimination and reaction time. He also measured how quickly people reacted which he later linked to internal wiring which ultimately limited intelligence ability. Throughout his research Galton assumed that people who reacted faster were more intelligent than others.
Composite photography Galton also devised a technique called "
composite portraiture" (produced by superimposing multiple photographic portraits of individuals' faces registered on their eyes) to create an average face (see
averageness). In the 1990s, a hundred years after his discovery, much psychological research has examined the
attractiveness of these faces, an aspect that Galton had remarked on in his original lecture. Others, including
Sigmund Freud in his work on dreams, picked up Galton's suggestion that these composites might represent a useful metaphor for an
Ideal type or a
concept of a "
natural kind" (see
Eleanor Rosch)—such as Jewish men, criminals, patients with tuberculosis, etc.—onto the same photographic plate, thereby yielding a blended whole, or "composite", that he hoped could generalise the facial appearance of his subject into an "average" or "central type". (See also entry
Modern physiognomy under
Physiognomy). This work began in the 1880s while the Jewish scholar
Joseph Jacobs studied anthropology and statistics with Francis Galton. Jacobs asked Galton to create a composite photograph of a Jewish type. One of Jacobs' first publications that used Galton's composite imagery was "The Jewish Type, and Galton's Composite Photographs",
Photographic News, 29, (24 April 1885): 268–269. Galton hoped his technique would aid medical diagnosis, and even criminology through the identification of typical criminal faces. However, his technique did not prove useful and fell into disuse, although after much work on it including by photographers
Lewis Hine,
John L. Lovell and
Arthur Batut.
Fingerprints The method of identifying criminals by their fingerprints had been introduced in the 1860s by Sir
William James Herschel in India, and their potential use in forensic work was first proposed by Dr
Henry Faulds in 1880. Galton was introduced to the field by his half-cousin
Charles Darwin, who was a friend of Faulds, and he went on to create the first scientific footing for the study (which assisted its acceptance by the courts) although Galton did not ever give credit that the original idea was not his. In a
Royal Institution paper in 1888 and three books (
Finger Prints, 1892;
Decipherment of Blurred Finger Prints, 1893; and
Fingerprint Directories, 1895), Galton estimated the probability of two persons having the same
fingerprint and studied the heritability and racial differences in fingerprints. He wrote about the technique (inadvertently sparking a controversy between Herschel and Faulds that was to last until 1917), identifying common pattern in fingerprints and devising a classification system that survives to this day. He described and classified them into eight broad categories: 1: plain arch, 2: tented arch, 3: simple loop, 4: central pocket loop, 5: double loop, 6: lateral pocket loop, 7: plain whorl, and 8: accidental. ==Views==